Resonant free piston Stirling engine systems are known in the art wherein the load apparatus is hydraulically driven from the periodic pressure wave of the engine, in such known systems the load apparatus is disposed within an incompressible fluid-filled space between a pair of flexible diaphragms which seal in and isolate the incompressible fluid, referred to hereafter as "hydraulic oil," from the Stirling engine. One of the diaphragms is arranged to be exposed to and acted on by the periodic pressure wave of the engine and the other diaphragm, acted on by the resulting pressure wave produced in the hydraulic oil, is arranged as part of a gas spring means. The pressure waves produced in the hydraulic oil are operative to reciprocally drive the movable member of the load apparatus in a direction along the same axis as that of the Stirling engine.
Such prior art engine-drive system assemblies were arranged in a stacked, coaxial relationship. While generally satisfactory from an operating standpoint, such prior art arrangements have typically been very long, causing mounting problems and preventing installation in conventional sized housing cabinets. In addition, in such prior arrangements all components of the load apparatus are disposed internally in the sealed oil-filled drive system making assembly of the load apparatus, as well as, maintenance, service, and repair both difficult and expensive. The present invention overcomes one or more of these prior art problems while also providing a more compact Stirling engine-load apparatus assembly.